1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, it relates to an apparatus and a method for correction of resist heating.
2. Description of Related Art
The microlithography technique which advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. Thus, the electron beam writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern.
FIG. 7 is a schematic diagram for explaining operations of a variable-shaped electron beam (EB) writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus operates as follows: A first aperture plate 410 has a quadrangular, such as a rectangular, opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 that has passed through the opening 411 into a desired rectangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 and thereby to irradiate a target workpiece or “sample” 340 mounted on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing. In other words, a rectangular shape capable of passing through both the opening 411 and the variable-shape opening 421 is used for pattern writing in the writing region of the target workpiece 340 on the stage. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method.
With development of optical lithography and tendency of wavelength shortening using EUV, the number of electron beam shots necessary for mask writing is increasing at an accelerated rate. Meanwhile, in order to maintain the accuracy of line width required for microminiaturization, it is planned to reduce shot noise or pattern edge roughness by increasing the dose of an electron beam by using a resist with low sensitivity. Thus, since the number of shots and the dose of irradiation are continuing to increase without end, the writing time also increases unlimitedly. Therefore, it is considered to shorten the writing time by increasing current density.
However, when providing irradiation energy of an increased quantity of electrons with higher current density in a short time, there is a problem of a phenomenon referred to as “resist heating” in which the resist sensitivity changes due to overheating of the substrate therefore the line width accuracy is degraded.